## 896. Monotonic Array

An array is monotonic if it is either monotone increasing or monotone decreasing.

An array `A` is monotone increasing if for all `i <= j`, `A[i] <= A[j]`.  An array `A` is monotone decreasing if for all `i <= j`, `A[i] >= A[j]`.

Return `true` if and only if the given array `A` is monotonic.

Example 1:

```Input: [1,2,2,3]
Output: true
```

Example 2:

```Input: [6,5,4,4]
Output: true
```

Example 3:

```Input: [1,3,2]
Output: false
```

Example 4:

```Input: [1,2,4,5]
Output: true
```

Example 5:

```Input: [1,1,1]
Output: true
```

Note:

1. `1 <= A.length <= 50000`
2. `-100000 <= A[i] <= 100000`

## Rust Solution

``````struct Solution;

impl Solution {
fn is_monotonic(a: Vec<i32>) -> bool {
let mut increasing = true;
let mut decreasing = true;
let n = a.len();
for i in 1..n {
if a[i] > a[i - 1] {
decreasing = false;
}
if a[i] < a[i - 1] {
increasing = false;
}
}
increasing || decreasing
}
}

#[test]
fn test() {
let a = vec![1, 2, 2, 3];
assert_eq!(Solution::is_monotonic(a), true);
let a = vec![6, 5, 4, 4];
assert_eq!(Solution::is_monotonic(a), true);
let a = vec![1, 3, 2];
assert_eq!(Solution::is_monotonic(a), false);
let a = vec![1, 2, 4, 5];
assert_eq!(Solution::is_monotonic(a), true);
let a = vec![1, 1, 1];
assert_eq!(Solution::is_monotonic(a), true);
}
``````

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